U.S. patent number 3,836,857 [Application Number 05/354,078] was granted by the patent office on 1974-09-17 for flame detector.
This patent grant is currently assigned to Hitachi, Ltd.. Invention is credited to Juichi Honda, Kazutoshi Ikegami, Motosi Miyanaka, Mitsuoki Yamamoto.
United States Patent |
3,836,857 |
Ikegami , et al. |
September 17, 1974 |
FLAME DETECTOR
Abstract
A flame detector wherein a pair of diodes are connected in
series with opposite directions of conduction across the respective
terminals of an AC power source, and a light emitting device, such
as a discharge tube, is connected between the point of connection
of the two diodes and a flame rod disposed in a flame to be
detected. With this construction, a predetermined voltage is
applied between a burner and the flame rod, whichever side of the
AC power source is grounded.
Inventors: |
Ikegami; Kazutoshi (Kokubunji,
JA), Honda; Juichi (Fujisawa, JA),
Miyanaka; Motosi (Yanai, JA), Yamamoto; Mitsuoki
(Suginami, JA) |
Assignee: |
Hitachi, Ltd. (Tokyo,
JA)
|
Family
ID: |
27292599 |
Appl.
No.: |
05/354,078 |
Filed: |
April 24, 1973 |
Foreign Application Priority Data
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May 12, 1972 [JA] |
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47-46406 |
May 12, 1972 [JA] |
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47-46407 |
May 12, 1972 [JA] |
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47-46408 |
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Current U.S.
Class: |
307/653; 307/650;
327/514; 340/579 |
Current CPC
Class: |
F23N
5/123 (20130101) |
Current International
Class: |
F23N
5/12 (20060101); H03k 003/26 (); G01n 027/00 () |
Field of
Search: |
;328/6,5,1 ;340/228.1
;315/53 ;451/15,25 ;307/310,311 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Rolinec; Rudolph V.
Assistant Examiner: Davis; B. P.
Attorney, Agent or Firm: Craig & Antonelli
Claims
What is claimed is:
1. A flame detector comprising a grounded burner, a flame rod
disposed at a place at which a flame from the burner is to exist,
first and second non-linear impedance means each presenting a low
impedance when a voltage is applied thereto and exhibiting a high
impedance when no voltage is applied thereo, an AC power source
having one of its terminals grounded, one of said terminals of said
power source being connected to one terminal of said first
non-linear impedance means and the other terminal thereof being
connected to one terminal of said second non-linear impedance
means, and a light emitting device for emitting light in response
to the presence to the flame, one of the electrodes of said light
emitting device being connected to said flame rod and the other
electrode being connected in common to the other terminal of each
of said first and second non-linear impedance means.
2. The flame detector according to claim 1, wherein each of said
first and second non-linear impedance means comprises a diode.
3. The flame detector according to claim 1, wherein each of said
first and second non-linear impedance means comprises a non-linear
photoconductive element having a high resistance when not
irradiated by light and presenting a low resistance when irradiated
by light, and a light emitting element formed integrally therewith,
said light emitting element being connected between one terminal of
said AC power source and ground, said photoconductive element being
connected between said one terminal of said AC power source and
said light emitting device.
4. The flame detector according to claim 3, wherein a capacitor for
bypassing AC signal components is connected across the terminals of
said light emitting device.
5. A flame detector comprising a grounded burner, first and second
flame rods disposed at a place at which a flame from the burner is
to exist, an AC power source one of its terminals grounded, and
first and second light emitting devices for emitting light in
response to the presence of the flame, said first light emitting
device being connected between said first flame rod and one of the
terminals of said AC power source, said second light emitting
device being connected between said second flame rod and the other
terminal of said AC power source.
6. The flame detector according to claim 5, wherein an individual
capacitor for bypassing AC signal components is connected across
both terminals of, and in parallel with, each light emitting
device.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a detector for flames, and more
particularly to a flame detector in which a light emitting device,
such as a discharge tube or a luminescent diode, is turned on and
off in response to the presence and absence of a flame.
In general, a flame detector exploiting the electric conductibility
or rectification action of a flame detects the presence of the
flame in such way that a voltage of several hundreds volts is
applied between a flame rod provided within the flame and a burner,
a minute current caused to flow via the flame between the flame rod
and the burner is amplified by an amplifier circuit of high input
impedance which employs a field-effect transistor or the like, or a
light emitting device, such as a neon tube, is caused to emit light
by the use of the minute current, and a photoconductive device
(such as a cadmium sulfide cell) is rendered operative by the
emitted light. As a power source for such a detector, the usual
commercial power supply can be directly used. Since, however, one
terminal of the commercial power supply is generally grounded and a
non-polarized type is often employed for a power plug socket, an
inconvenience results in that no voltage is applied in one of the
directions in which the plug socket is inserted in the power outlet
(because the burner is generally grounded). For this reason, in the
prior art, the voltage to be applied between the flame rod and the
burner must be supplied through a transformer from the power
source. The transformer isolates the primary and secondary sides in
a DC sense, so that even when one of the primary side terminals is
grounded, a voltage on the secondary side floats from ground. An
appropriate voltage is accordingly applied between the flame rod
and the burner irrespective of the direction in which the power
plug socket is inserted in the power outlet.
The provision of the transformer as stated above, however, has the
disadvantages of making the flame detector large in volume, as well
as in weight, and high in cost.
SUMMARY OF THE INVENTION
It is accordingly an object of the present invention to provide a
novel flame detector which is free from the disadvantages of the
prior art as mentioned above.
Another object of the present invention is to provide a flame
detector which is constructed such that both terminals of a power
source are connected to one terminal of a light emitting device
through respective diodes, while the other terminal of the light
emitting device is connected to a flame rod.
Another object of the present invention is to provide a flame
detector which employs a composite element comprising a light
emitting element and a photoconductive element integrally coupled,
thereby to make the previously required power transformer
unnecessary.
Still another object of the present invention is to provide a flame
detector which is constructed such that two flame rods are disposed
in a flame, and that one of the terminals of a power source is
connected through the first light emitting device to one of the
flame rods, while the other terminal of the power source is
connected through the second light emitting device to the other
flame rod.
The other objects, features, and advantages will be apparent from
the following detailed description when read in conjunction with
the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a circuit diagram showing an embodiment of a flame
detector of the present invention;
FIG. 2 is a circuit diagram showing an example of a flame detecting
and control apparatus to which the flame detector of the present
invention is applied; and
FIGS. 3 and 4 are circuit diagrams each showing other embodiments
of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In FIG. 1 showing an embodiment of the present invention, numeral 8
designates an AC power source which is grounded at either of the
terminals A or B ("OR" in the figure signifies that either terminal
is grounded). Diodes 6a and 6b are connected in series with
opposite directions of conduction across the respective terminals
of the AC power source. A voltage is therefor provided at the
juncture C between the diodes. Accordingly, whichever terminal A or
B is grounded, the rectified voltage of the AC power source 8 is
obtained at the point C through the diode connected to the terminal
which is not grounded. Through a detecting device 5, the voltage is
applied between a flame rod or detecting electrode 3 and a burner
1, which is grounded. A current flows between the burner 1 and the
flame rod 3 via a flame 2. The detecting device 5 is thereby
rendered operative (in the embodiment in FIG. 1, a discharge tube
is lit). Thus, the presence of the flame 2 is detected. A
protective resistance 4 is provided for the case where the burner 1
and the flame rod 3 erroneously come into contact.
FIG. 2 is a circuit diagram of flame detecting and control
apparatus which makes use of the flame detector of the present
invention. Referring to the figure, in case of ignition, a power
switch (not shown) is first turned on to connect the power source
8. Upon connection of the power source 8, a timer 9 is actuated.
Contacts 9 - 1 and 9 - 2 of the timer 9 are so set as to initially
turn on and to turn off after a fixed time. Accordingly, the power
source 8 is connected through the contact 9 - 2 to a coil 10 of a
standard magnet valve (not shown), the magnet valve is opened, and
a gas is ejected from the burner 1. Since a transfer contact 16 - 1
of a relay 16 is connected on the side D at this time, the voltage
of the power source 8 is applied onto the primary side of a
high-tension transformer for ignition 11. A high voltage is induced
on the secondary side of the transformer 11, to give rise to a
spark discharge between a discharge electrode for ignition 12 and
the burner 1. The gas is thereby ignited. In the case where the
ignition fails for any cause, the opening of the contacts 9 - 1 and
9 - 2 of the timer 9 after a fixed time will close the magnet valve
to stop the gas and to arrest the spark discharge. Whichever
terminal A or B of the power source 8 is grounded, the rectified
voltage is produced at the point C through the diode 6a or 6b,
connected to the other terminal which is not grounded. The voltage
is applied through the discharge tube 5 between the flame rod 3 and
the grounded burner 1. Therefore, in the case where the ignition is
normally effected with no misfiring, the current flows via the
flame 2 between the flame rod 3 and the burner 1, to light the
discharge tube 5. The resistance of a cadmium sulfide cell 13 is
thereby decreased, transistors 14 and 15 are brought from the "off"
state into the "on" state, and the relay 16 is energized.
The changeover contact 16 - 1 of the relay 16 is so set as to be
connected to the side D for the "off" state of the transistor 15
and to the side E for the "on" state. Accordingly, when the
ignition is normally effected and the relay 16 is energized, the
primary side of the igniting high-tension transformer 11 turns off
to stop the discharge. If the burning is normally carried out, the
current continually flows via the flame 2 between the burner 1 and
the flame rod 3, to keep the relay 16 energized. On the other hand,
the contacts 9 - 1 and 9 - 2 of the timer 9 are opened by the
operation of the timer after a fixed time, as has been previously
stated. In this case, the magnet valve coil 10 is connected to the
power source 8 by the contact 16 - 1 of the relay 16, so that the
burning is continued.
In the case where the flame is extinguished by any cause during the
burning, the current between the flame rod 3 and the burner 1
vanishes. The illumination of the discharge tube 5 is therefore put
out to turn off the transistor 15, with the result that the contact
16 - 1 of the relay 16 is reset onto the side D. Accordingly, since
the timer 9 has already caused switch 9 - 2 to open, the magnet
valve coil 10 is deenergized, the solenoid valve is closed, and the
gas supply is stopped. Reference numeral 17 in FIG. 2 indicates a
power source for operating the transistors 14 and 15 and the relay
16.
FIG. 3 is a circuit diagram showing another embodiment of the
present invention, which permits elimination of the rectifiers 6a
and 6b. Numeral 8 designates an AC power source which is grounded
at either of the terminals A or B ("OR" in the figure signifies
that either one is grounded). Composite elements 20a and 20b, the
former comprising a light emitting element 19a and a
photoconductive element 18a and the latter comprising a light
emitting element 19b and a photoconductive element 18b, are
connected across the respective terminals of the AC power source 8.
Each of the light emitting elements 19a and 19b is grounded at one
end, while the output ends of the photoconductive elements 18a and
18b are connected together at a point C. Accordingly, whichever
terminal A or B is grounded, an AC voltage from the power source 8
is obtained at the point C in such a manner that the light emitting
element in the composite element connected to the terminal which is
not grounded emits light to thereby bring the photoconductive
element in the identical composite element into the conductive
state. In that case, the light emitting element in the composite
element connected to the terminal on the ground side has no voltage
applied thereto, and does not emit light. Accordingly, the
photoconductive element in the identical composite element exhibits
a very high resistance, and is in the nonconductive state.
When the voltage is applied through a detecting element 5 between a
detecting electrode or flame rod 3 and a grounded burner 1, a
current is permitted to flow via a flame 2 between the flame rod 3
and the burner 1. The detecting element 5 is thereby rendered
operative (in FIG. 3, a discharge tube is lit). Thus, the presence
of the flame 2 is detected.
A capacitor 7 connected in parallel with the detecting element 5 is
effective in the case where the rectification action of the flame
is utilized. When the impedance of the capacitor 7 is made
sufficiently low as compared with the resistances of the protective
resistors 4a, 4b, 21a, and 21b, the capacitor constitutes a bypass
circuit for AC components. Therefore, in the case where an AC
current flows through the detecting circuit (in such case where the
flame rod is erroneously grounded), the detecting device 5 does not
operate. The detecting device 5 is rendered operative only by the
DC component which is produced by the rectifying action of the
flame. It is accordingly possible to prevent the detecting device
from erroneously operating at such undesirable conditions as
grounding of the flame rod.
FIG. 4 shows a further embodiment of the present invention wherein
rectifiers are not required. Referring to the figure, numeral 8
represents an AC power source which is grounded at either of the
terminals A or B ("OR" in the figure means that either one is
grounded). A first circuit in which a detecting electrode or flame
rod 3a, protective resistance 4a, and a detecting device 5a are
connected in series, and a second circuit in which a detecting
electrode or flame rod 3b, protective resistance 4b, and a
detecting device 5b are connected in series, are connected across
the respective terminals of the power source 8.
Accordingly, depending on which terminal A or B is grounded, the
voltage of the power source 8 is applied between the flame rod 3a
or 3b connected to the terminal not grounded and the grounded
burner 1. A current is accordingly caused to flow via the flame 2
between the flame rod 3a or 3b and the burner 1, so that the
corresponding detecting device 5a or 5b is made operative (in FIG.
4, a discharge tube is lit). In this way, the presence of the flame
2 is detected. A capacitor 7a or 7b connected in parallel with the
detecting device 5a or 5b serves as bypass components for AC
components, as described in connection with the embodiment of FIG.
3. Owing to the bypass circuit, in the case where an AC current
flows through the detecting circuit (in such case where the flame
rod is erroneously grounded), the detecting device is not operated.
The detecting device is operated only by the DC component which is
created by the rectifying action of the flame. It is accordingly
possible to prevent the detecting device from damage which might
result from grounding of the flame rod.
While the embodiments of FIGS. 3 and 4 are described in the absence
of control circuitry to control the starting and continuing
operation of the burner, it should be understood that these
embodiments may be used with the control apparatus formed by
elements 9 through 17 in FIG. 2 or any other suitable control
apparatus.
As described above, the present invention makes it possible to use
the usual commercial power supply as the power source of the
detecting circuit without employing a power transformer for the
detector circuit. The flame detector of the present invention
accordingly has the advantages of being light in weight, low in
cost and capable of reliably detecting a flame by exploiting the
electric conductibility or the rectifying property induced between
the flame rod and the burner by the presence of the flame. It can
be utilized in a variety of equipment, such as an oil burner, heavy
oil combustion equipment, an instantaneous water boiler and a gas
bath, for example.
* * * * *